Get the Hippo... it has an AFC.
Pro Ring has an air flow control too by design, I tried to explain it but it seems nobody understands it, because it is too understated, but that is the way we designed it
I have a Hippo attached to one of my Provari and I have a Pro Ring for my second Provari. I use them both and I am happy with them.
What Phil didn't explain is that you have to unscrew the Pro Ring from the bottom cap in order to close the air flow and you can adjust it also, because it is designed that way. The opposite would be wrong. Anybody who has the Pro Ring can confirm it.
Below are my 2 Provari with 2 SnP, a GP SnP with experimental gold plated 23 mm covers and Hippo and the a GP SnP with experimental titanium tank, a 22 mm top cover and Pro Ring.

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